1. Field of the Invention
The present invention relates to a rubber crawler used in the condition that is rotatably connected around a driving roller and a driven roller, particularly a coreless rubber crawler in the form of endless belt having main cords and bias cords embedded therein.
2. Description of the Related Art
Usually, a coreless rubber crawler is frequently used for a high-speed running vehicle because the crawler shows a reduced vibration and running resistance as compared with a core-embedded rubber crawler. However, the coreless rubber crawler has a poor transverse stiffness as compared with the core-embedded rubber crawler, and therefore main cords and further bias cords are embedded in the coreless rubber crawler.
In case the main cords (i.e., main cord layer) and bias cords (i.e., bias cord layer) are embedded in a rubber crawler in the form of endless belt, there is generated torsion (meandering) in the width direction which is caused by extension angles of cords of the cord layers and return force of twist of the cords when the rubber crawler is driven in the running direction by the driving rollers. In the worst case, there is possibility that the rubber crawler disconnects from the driving and driven rollers.
To solve the above problems, JA 1 O-59228 discloses a first conventional core-embedded rubber crawler wherein steel twist wires are extended in the peripheral direction (lengthwise direction) between the core member and the ground surface of the rubber crawler, the steel twist wires comprising an S-twist wire and a Z-twist wire arranged alternately such that the adjacent twist wires compensate torsion caused by return force of twist of each of the twist wires.
Further, FIG. 7 illustrates a second conventional rubber crawler as disclosed in JA11-301536, which was filed by the present applicant. In the crawler, cord layers 102Z, 102S, which are wound in the directions opposite to each other, are arranged so as to be adjacent to each other in the crosswise direction whereby torsion moments caused by the wound tensions are compensated each other.
Furthermore, FIGS. 8 and 9 illustrate a third conventional rubber crawler, which was similarly filed by the present applicant. In the crawler, a main cord layer 204 extended in the lengthwise direction and a bias cord layer consisting of plural cords 205, 206 superposed on the main cord layer 204 are embedded in the rubber crawler, the plural cords 205, 206 having extension angles of the cords in the directions opposite to each other on the same plane of the plural cords 205, 206.
In a rubber crawler driving device wherein the above rubber crawler 201 in the form of endless belt is rotatably connected around a driving roller 210 and a driven roller 211, the diameters of the driving roller 210 and driven roller 211 are reduced against the direction of sharing torsion force which is generated in the rubber crawler 201 by tension caused by driving of the crawler owing to the angles of the cords of the bias cords 205, 206. This reduction of the diameters compensates the sharing torsion force to ensure running stability without shift (deviation) in the crosswise direction.
However, though, in the core-embedded rubber crawler of the first conventional example, the S-twist wire and Z-twist wire arranged alternately compensate the return force of twist of the twist wires by the twist wires adjacent to each other, the crawler is not capable of compensating the shift (deviation) of the crawler generated in the width direction of the driving or driven roller owing to some cause, for example, force generated when the crawler collides with an obstacle on a road surface. Hence, it is required that a guide projection is formed on the core to prevent the crawler from disconnecting from the rollers, whereby the rubber crawler is obliged to be complicated in its structure and increased in its weight.
In the second conventional example of FIG. 7, the cord layers 102Z, 102S wound in the directions opposite to each other are embedded so as to be adjacent to each other in the width direction whereby torsion moments caused by the wound tensions can be compensated each other. Further, in case the crawler is shifted in the width direction of the driving or driven roller owing to some cause, the tractive drive in the running direction of the rubber crawler resulted from driving of the driving roller generates torsion (meandering) in the width direction depending on extension angles of cords of the cord layer, whereby the shift (deviation) in the width direction is compensated to restore to the original state. However, a complicated winding machine and complicated processes are needed for winding spirally a long cord as above.
Furthermore, in the third conventional example of FIG. 8, the good combination of the plural cords 205, 206 having extension angles of the cords in the directions opposite to each other on the same plane and the diameters of the driving roller 210 and driven roller 211 reduced in the outer direction of the axis of the rollers compensates the sharing torsion force to ensure running stability without shift (deviation) in the crosswise direction. However, it is required to combine the driving roller 210 with the driven roller 211, both the rollers having special shape, and therefore it is difficult to apply the above technique to a driving device provided with usual rollers.